A bumper arrangement for motor vehicles, particularly passenger cars, having a bumper and flexible fastening devices by which the bumper is held on the vehicle body at a changeable distance from the vehicle body. In the case of distance changes in a first distance area, the flexible fastening devices can essentially regenerate. The bumper arrangement has impact absorbing tubes which act as supporting devices in the event of distance reductions in a second area which is closer to the vehicle body than the first distance area. In the event of a pressure load in the longitudinal direction of the tubes, the tubes act as supporting devices while being essentially unable to regenerate while the tube wall is destroyed on the tube end side and the tube wall material is deflected in the transverse direction.
A bumper arrangement of the above-described type is known from the German Patent Document DE-A 24 41 557 (FIGS. 6, 8), in which hydraulic shock absorbers are provided as flexible fastening devices. The cylinder housing of each shock absorber fastened to the vehicle body forms an impact absorbing tube which, in the case of a further pushing-together of the cylinder housing and the piston rod in the second distance area from the piston rod closer to the vehicle body which exceeds the flexible compression in the first distance area farther removed from the vehicle body, can be expanded by means of a projection existing on the piston rod. So that the cylinder housing will tear open in a defined manner when the projection is pressed in, the cylinder housing may be provided with longitudinal notches. The strips of the cylinder housing wall, which form during the expanding, are deflected in the radial direction toward the outside by the projection on the piston rod and roll up spirally similar to metal shavings during a cutting operation so that the cylinder housing opens up radially from the direction of its bumper-side end. The site of the expansion shifts in the longitudinal direction of the cylinder housing, and the expansion takes place on the respective, momentarily existing end of the cylinder housing which shortens corresponding to the progression of the expanding. The length along which the expanding takes place is a function of the extent of the effective kinetic energy and of the structural design of the bumper arrangement and its arrangement on the vehicle body which, in a holding manner, reaches around the body-side area of the cylinder housing and counteracts an expansion of this area of the cylinder housing. In the case of an impact, the bumper arrangement can elastically absorb the kinetic energy up to a first threshold value, for example, of an impact speed of 8 km/h, and can regenerate automatically after the impact. At higher impact speeds, the bumper arrangement can absorb the kinetic energy no longer only elastically but, up to a second threshold value, for example, of an impact speed of 15 km/h, while the impact absorbing tubes are destroyed which are plastically deformed. In the case of impact speeds up to the second threshold value, the vehicle body protected by the bumper arrangement is therefore not damaged.
It is an object of the invention to provide a bumper arrangement which may have small dimensions, particularly a small overhang in the driving direction and a low weight and, in addition, after a destruction of the impact absorbing elements which took place in the second distance area, can be restored at low expenditures in an operationally appropriate manner.
This and other objects are achieved by the present invention which provides a bumper arrangement for a motor vehicle having a vehicle body, comprising a bumper, at least one fastening device by which the bumper is held on the vehicle body at a changeable distance, and which can essentially regenerate after the distance changes within a first distance area, and impact absorbing tubes. The impact absorbing tubes act as supporting devices for distance changes within a second distance area that is nearer to the vehicle body than the first distance area. In the event of a pressure load in a longitudinal direction of the tube, the impact absorbing tubes act as supporting devices and are unable to regenerate. The impact absorbing tubes having tube walls, these tube walls being destroyed on a tube end side in the event of a pressure load and the material of the tube wall being deflected in a transverse direction. The impact absorbing tubes are parts separate from the at least one fastening device and consist of at least one fiber composite, with fibers of the fiber composite arranged at least essentially in the longitudinal direction of the tube. As a result of the present invention, an effective energy absorption is achieved by means of simple devices while using low-cost components. The bumper arrangement according to the invention permits a liberal design, particularly also of its components, can be easily mounted during the manufacturing of the motor vehicle and is easy to repair. It requires little space and can easily be adapted to varying requirements by the use of correspondingly designed components. In addition, it is not very susceptible to disturbances, and its impact absorbing tubes are not endangered by corrosion.
The impact absorbing tubes can easily be manufactured at low cost. It is particularly advantageous to manufacture the impact absorbing tubes by the cutting of extruded tube sections into lengths.
It is particularly advantageous to use spring elements as flexible fastening devices which essentially have a ring shape and also consist of at least one fiber composite. Spring elements of this type, which are loaded in the transverse direction and which, at a low load, have an elastic effect and can regenerate, and, at a higher load, like the impact absorbing tubes, act as impact absorbing elements while being destroyed and can essentially not regenerate. Such spring elements are known from the German Patent Document DE-OS 36 26 150. By means of the parallel arrangement of the spring elements and of the impact absorbing tubes, a particularly favorable energy absorption is obtained.
The arrangement of an impact absorbing tube or several impact absorbing tubes in a spring element results in a compact construction.
Although it is known from the European Patent Document EP-PS 55 364 to manufacture an impact protection component for the support of a motor vehicle bumper as a tube from at least one fiber composite, the tube wall is constructed as a network. The tube is used as an elastic (reversible) support in the case of low pressure loads in the longitudinal direction of the tube, and in the case of higher loads, irreversibly absorbs energy while permanently deforming, and is therefore used for the flexible support as well as as an impact absorbing tube.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.